IntrusivePtr.useCount

static struct Foo{
    ControlBlock!(int, int) c;
    int i;

    this(int i)pure nothrow @safe @nogc{
        this.i = i;
    }
}


IntrusivePtr!Foo x = null;

assert(x.useCount == 0);

x = IntrusivePtr!Foo.make(123);
assert(x.useCount == 1);

auto y = x;
assert(x.useCount == 2);

auto w1 = x.weak;    //weak ptr
assert(x.useCount == 2);

IntrusivePtr!Foo.WeakType w2 = x;   //weak ptr
assert(x.useCount == 2);

y = null;
assert(x.useCount == 1);

x = null;
assert(x.useCount == 0);
assert(w1.useCount == 0);